This invention relates to a tibial prosthesis for implantation in a surgically prepared cavity in a tibia of a patient undergoing knee replacement.
Tibial prostheses are commonly made in two parts, namely a metal tray-shaped component with a stem projecting from a lower side thereof for insertion in a surgically prepared cavity in a tibia of a patient requiring a tibial surface replacement operation and with an upstanding peripheral rim and a tibia insert which is typically made from ultra high molecular weight polyethylene that fits on top of the tray component and is located in place inter alia, by means of the upstanding peripheral rim.
There are typically 6 sizes of the metal tray-shaped component to account for variations in tibia bone size and 5 thicknesses of tibia insert to account for variation in the amount of bone resected and laxity of the collateral ligaments. Tibia inserts typically also come in 2 or 3 sizes to best fit the range of metal tray sizes. Tibia size and insert thickness are unrelated; therefore there are many possible combinations of assembled components, depending on the specific surgical requirements.
Various locking arrangements for locking the tibia insert in place on top of the metal tray portion have been proposed. Thus many total and uni-compartmental knee replacements have a clip mechanism to fit the insert to the tray, which the surgeon assembles, as a modular series of parts. However, the existing clip mechanisms have the disadvantage that, since the tibia insert is merely clipped into place, there is room for motion since only the clip portion of the tibia insert resists such motion. Thus, although the surgeon may feel the insert clip into place and it may seem that the insert is not moving easily, such mechanisms do in fact allow relative movement between the tray and insert when the prosthesis is loaded as the patient walks or takes other exercise after implantation has been effected. Such motion causes so-called “backside wear” which exacerbates the phenomenon of debris-induced osteolysis. The effects of modular tibial insert micromotion have been reported, for example, by Nancy L. Parks et al., Clinical Orthopaedics and Related Research, Number 356, pages 10 to 15 (1998). Other papers highlighting the problems of existing tibial prostheses include those by Gerard A. Engh et al., The Journal of Bone and Joint Surgery, Volume 83-A, Number 11, November 2001, pages 1660 to 1665; Ray C. Wasielski et al., Clinical Orthopaedics and Related Research, Number 345, pages 53 to 59 (1997); Jack M. Bert et al., The Journal of Arthroplasty, Volume 13, No. 6 (1998), pages 609 to 614; William D. Bugbee et al., Clinical Orthopaedics and Related Research, Number 348, pages 158 to 165 (1998); Paul A. Peters et al., The Journal of Bone and Joint Surgery, Vol. 74-A, No. 6 (July 1992), pages 864 to 876; Aaron G. Rosenberg et al., Orthopedic Clinics of North America, Vol. 20, No. 1 (January 1989(, pages 97 to 110; and Leo A. Whiteside, Orthopedic Clinics of North America, Vol. 20, No. 1 (January 1989), pages 113 to 124.
A few designs of tibial prostheses are sold in the form of compression moulded plastics material units and metal backs which are assembled as one piece units in the factory. However, although such moulded one piece knee components overcome the problems associated with micromotion, a significant drawback to their widespread use is the problem of storing the large volume of stock that must be held by a hospital due to the need for all size and thickness options being required on the shelf for each operation.
On the other hand the systems which allow the surgeon to clip together a tibia and a tray avoid this storage problem by allowing choice of many variants of metal tray and tibia insert.
There is a large volume of patent literature describing tibial prostheses, including U.S. Pat. No. 5,080,675 (Lawes et al.), U.S. Pat. No. 4,944,757 (Martinez et al.), U.S. Pat. No. 4,938,769 (Shaw), U.S. Pat. No. 4,936,853 (Fabian et al.), U.S. Pat. No. 4,714,474 (Brooks, Jr. et al.), U.S. Pat. No. 4,711,639 (Grundei), U.S. Pat. No. 4,257,129 (Volz), U.S. Pat. No. 4,219,893 (Noiles), U.S. Pat. No. 4,207,627 (Cloutier), U.S. Pat. No. 4,016,606 (Murray et al.), U.S. Pat. No. 6,126,692 (Robie et al.), U.S. Pat. No. 5,702,464 (Lackey et al.), U.S. Pat. No. 5,702,463 (Pothier et al.), U.S. Pat. No. 5,645,604 (Schneider et al.), U.S. Pat. No. 4,950,298 (Gustilo et al.), U.S. Pat. No. 5,370,699 (Hood et al.), U.S. Pat. No. 4,795,468 (Hodorek et al.), U.S. Pat. No. 4,673,408 (Grobbelaar), U.S. Pat. No. 4,550,448 (Kenna), U.S. Pat. No. 5,458,637 (Hayes), U.S. Pat. No. 5,405,396 (Heldreth et al.), U.S. Pat. No. 5,344,460 (Turanyi et al.), U.S. Pat. No. 5,194,066 (Van Zile), U.S. Pat. No. 5,192,328 (Winters), U.S. Pat. No. 5,108,442 (Smith), U.S. Pat. No. 5,062,852 (Dorr et al.), U.S. Pat. No. 5,007,933 (Sidebotham et al.), U.S. Pat. No. 4,963,152 (Hofmann), U.S. Pat. No. 4,822,362 (Walker et al.), U.S. Pat. No. 4,673,407 (Martin), U.S. Pat. No. 4,470,158 (Pappas et al.), U.S. Pat. No. 4,462,120 (Rambert et al.), U.S. Pat. No. 4,216,549 (Hillberry et al.), U.S. Pat. No. 3,958,278 (Lee et al.), and U.S. Pat. No. 3,868,730 (Kaufer et al.).
There is a need in the art for a tibial prosthesis formed from a metal tray component and a plastics material tibia insert which can be assembled in an operating theatre by a surgeon in the course of a total or partial knee replacement operation and which will, after assembly and implantation in a patient's knee, substantially obviate the problems of micromotion between the two components of the prosthesis and potential exacerbation of debris-induced osteolysis.